1. Field of the Invention
The present invention relates to a planar light source and a backlight unit including the same, and more particularly, to a planar light source, which can achieve a uniform luminance distribution and high efficiency while using a decreased number of light emitting devices by optimizing an arrangement and an interval of the light emitting devices.
2. Description of the Related Art
A cold cathode fluorescent lamp (CCFL) is used as a light source of a related art backlight unit of a liquid crystal display (LCD). However, the CCFL uses a mercury gas, which may contaminate the environment. The CCFL also has limitations of slow response time and low color reproducibility and besides is not appropriate for a slim and light LCD panel.
Compared to the CCFL, light emitting diodes (LEDs) are ecological, and are useful for video signal streams and capable of impulsive driving because of its quick response time of a few nano seconds. The LEDs have color reproducibility of 100% or higher and allow arbitrary changes in luminance, a color temperature or the like through the control of the quantity of light of red, green and blue LEDs. Besides, they are suitable for slim and light LCD panels. For these reasons, the LED is being widely used as a light source for a backlight unit of an LCD panel or the like.
LCD backlight units employing the LEDs may be categorized into edge-type backlight units and direct-type backlight units according to locations of light sources. In the edge-type backlight unit, a horizontally elongated bar-type light source is placed at an edge side to emit light to an entire surface of an LCD panel through a light guide plate. In the direct-type backlight unit, a planar light source having almost the same area as the LCD panel is placed under the LCD panel to emit light directly to the entire surface of the LCD panel.
FIG. 1 is a plan view illustrating an arrangement of light emitting devices in a related art planar light source.
As shown in FIG. 1, a planar light source 100 used in the related art direct type LCD panel has a structure in which a plurality of LEDs 102 are arranged in rows and columns on a substrate 101. In this case, adjacent LEDs 102 have a pitch (x) in an x-direction and a pitch (y) in a y-direction that are equal to each other. Thus, adjacent four LEDs 102 of the plurality of LEDs 102 form a regular square.
This arrangement of the LEDs 102 is inefficient because more LEDs than needed are used in order to cover a light emitting area.
Besides, there may be a great difference in luminance between an area adjacent to the LEDs 102 and an area located away from the LEDs 102, i.e., a very center of the square formed by four LEDs 102. That is, if a large number of LEDs 102 are arranged, uniform luminance can be achieved. However, if the number of LEDs is reduced for the improved efficiency, the distance between adjacent LEDs is increased, which may change the luminance distribution.
Therefore, with respect to a planar light source used for an LCD panel or the like, there is a need for a method for improving efficiency of the planar light source by reducing the number of light emitting devices used therein while securing small variations in luminance, i.e., uniform luminance.